Automated marine navigation

ABSTRACT

Autonomously piloting a sea-faring vessel traveling on a pre-defined course at a nominal speed includes: measuring a slamming parameter of the vessel; determining that the slamming parameter is outside an acceptable range; and autonomously decreasing the speed of the vessel until the slamming parameter is within the acceptable range, thereby causing the vessel to enter a reduced-speed mode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/201,429 filed on Mar. 15, 2021, the entire content of which is herebyincorporated by reference.

BACKGROUND OF THE INVENTION

Techniques for autonomous navigation of sea-faring vessels is known inthe art. However, many such techniques do not account for the comfort orsafety of passengers or equipment, thereby limiting adoption ofautomated sea-faring vessels.

SUMMARY OF THE INVENTION

In general, in one aspect, autonomously piloting a sea-faring vesseltraveling on a pre-defined course at a nominal speed includes: measuringa slamming parameter of the vessel; determining that the slammingparameter is outside an acceptable range; and autonomously decreasingthe speed of the vessel until the slamming parameter is within theacceptable range, thereby causing the vessel to enter a reduced-speedmode.

Implementations may have one or more of the following features: Theslamming parameter includes a time rate of change of the vessel's heave.The slamming parameter includes a pitch angle of the vessel. Theslamming parameter includes a slamming force experienced by the vessel.Also includes exiting reduced-speed navigation mode after the expirationof a pre-determined time interval, wherein exiting reduced-speed modeincludes increasing the vessel's speed until either (a) the slammingparameter falls within the acceptable range, or (b) the vessel returnsto its nominal speed.

In general, in another aspect, autonomously piloting a sea-faring vesseltraveling on a pre-defined course includes: measuring a roll parameter;determining that the roll parameter is outside an acceptable range; andautonomously determining an updated course that includes one or moretacking legs, in which each tacking leg makes a corresponding tackingangle with respect to the nominal course, thereby entering the vessel ina tacking mode.

Implementations may have one or more of the following features: Eachtacking angle of each tacking leg is determined by incrementing anintermediate tacking angle of the vessel until either (a) a maximumtacking angle is reached, or (b) the roll parameter is within theacceptable range. The updated course includes at least one turningmaneuver. The turning maneuver is initiated immediately following a peakin a wave's contact force on the vessel. The wave contacting the vesselis detected by the occurrence of a local extremum in a pitch angle ofthe vessel. The roll parameter includes a roll angle of the vessel. Theroll parameter includes a time rate of change of a roll angle of thevessel.

These and other aspects may be expressed in methods, systems, sea-faringvessels, or other forms. Other features and advantages of the inventionare apparent from the following description, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a coordinate system.

FIG. 2 is an overhead view of a vessel undergoing slamming.

FIG. 3 is a side view of a vessel undergoing slamming.

FIG. 4 is an overhead view of a vessel undergoing rolling.

FIG. 5 is a side view of a vessel undergoing rolling.

FIG. 6 is a block diagram of a navigation system.

FIG. 7 is a flowchart of a process for mitigating slamming.

FIG. 8 is a flowchart of a process for mitigating rolling.

FIG. 9 is an overhead view of a roll-mitigated course.

DETAILED DESCRIPTION

Overview

A sea-faring vessel 100 can experience motion with respect to threeaxes, as shown in FIG. 1. Rotational motion along the respective axesshown in FIG. 1 is called yaw, pitch, and roll. Translational motion inthese axes is called, respectively, heave, sway, and surge.

Although extreme translational or rotational motion along any axis canbe uncomfortable for any onboard passengers, certain extreme motions canbe particularly dangerous. For example, extreme heave or extreme pitchcan result in dangerously increased stress on load-bearing structures inthe vessel 100, can result in damage to onboard equipment or injury toonboard personnel, or can result in the vessel foundering, taking onexcess water, or other undesirable consequences. Extreme heave and/orpitch is also known as “slamming.”

Extreme rolling motion can also be particularly dangerous: it presents arisk to cargo or reactionary forces to the vessel caused by cargomotions, for movement of unsecured or inadequately secured equipment, arisk of on-board personnel falling, and in extreme cases can result inthe vessel taking on excess water, becoming swamped, or capsizing.

FIG. 2 is an overhead view of a vessel undergoing slamming, and FIG. 3is the corresponding side view. In FIG. 2, a vessel 200 is travelingwith a velocity v_(vessel) (with respect to any fixed reference frame;e.g., with respect to the ground which is assumed for the purposes ofillustration to be at rest), and is traveling through a series of waveshaving wavefronts 202 traveling with velocity v_(wave) relative to theground.

Referring to FIG. 3, as a wavefront 202 and the vessel 200 pass eachother, the vessel pitches upwards to meet the wave surface. Then thevessel's velocity carries it over the wave's crest, such that a gap ofdistance d emerges between the bottom surface of the vessel 200 and thetop of the water. In turn, the vessel 200 experiences an extreme changein pitch angle and/or heave, followed by an extreme deceleration or anabrupt stop to this motion as the vessel re-establishes contact with thesurface of the water.

The maximum distance d experienced by a vessel as it traverses a wave isone way to measure the magnitude of the slamming that the vessel 200 isexperiencing. Moreover, this maximal d is correlated with the differencein velocity |v_(vessel)−v_(wave)|. In particular, reducing this velocitydifference is operable to reduce the maximal distance d, andconsequently to mitigate the adverse effects of slamming.

FIG. 4 is an overhead view of a vessel undergoing rolling, and FIG. 5 isthe corresponding side view. In this case, a vessel 400 is travelingwith velocity v_(vessel), and a series of wavefronts 402 are approachingwith velocity v_(wave) perpendicular to the vessel. As shown in FIG. 5,the wavefront 402 impacts the vessel 400 and imparts a rolling motion,causing the vessel to deviate from its stable upright position (asindicated by the dashed line 404).

The degree to which an incoming wave imparts a rolling motion to thevessel depends in part on the angle the wave makes with the vessel.Thus, one way to mitigate the roll induced by the wavefront 402 is byaltering (i.e., decreasing) the angle that the vessel 400 makes to thewavefront or wave direction.

The techniques described below implement these general observations inthe context of autonomous or semiautonomous sea-faring vessels. Amongother things, employing the techniques described below, a sea-faringvessel can mitigate the adverse effects of extreme slamming and/orrolling without human intervention and/or initiation of thesetechniques.

Implementations

FIG. 6 is a block diagram of an autonomous navigation system. Asexplained more fully below, the navigation system 600 can be implementedas software, hardware, or a combination of hardware and software. Insome implementations, the navigation system 600 is implemented as astandalone computing device (with accompanying software) that may bedeployed on “general purpose” sea-faring vessels; that is, vessels thatwere not specifically designed to accommodate autonomous navigationfunctionality.

The navigation system 600 includes a sensor module 602. The sensormodule is operable to interface with various sensors either onboard avessel or remote from a vessel. In some implementations, the sensors mayinclude accelerometers and/or gyroscopes that measure the motion of thevessel, a component thereof, or an object therein (including but notlimited to cargo). In some implementations, the sensors may include oneor more cameras that are configured to acquire still images or video;e.g., images or video of incoming waves or the waters surrounding thevessel. In some implementations, the sensors can include one or moreactive or passive radio sensing systems, operable to sense theposition(s) and/or motion(s) of other nearby vessels or other objects ofinterest. In some implementations, the sensors could include globalpositioning satellite (“GPS”) receivers, operable to sense the positionof the vessel with respect to the Earth. (This may be useful, e.g., toutilize external characterizations of the waters surrounding thevessel.) In some implementations, the sensors may include one or moremarine Automatic Identification System (“AIS”) receivers, operable toidentify AIS signals sent by nearby vessels. In some implementations,the sensors may include radar sensors. In some implementations, thesensors include instruments for measuring weather conditions (e.g., oneor more anemometers for measuring wind speed; one or more barometers formeasuring atmospheric pressure, one or more thermometers for measuringtemperature, etc.) In some implementations, the sensors includevolumetric sensors operable to determine the amount of fluid in one ormore points of a fluid reservoir. Other sensors are possible.

The navigation system 600 includes a communications module 604. Thecommunications module is operable to facilitate communication betweenthe navigation system 600 and external sources, command station, ordestinations. In some implementations, the communications module 604includes equipment suitable for electronic communications with otherequipment, either onboard the vessel or remote from the vessel. In someimplementations, the communications module 604 includes one or moreantennas suitable for cellular or data communication with other nearbyvessels, with points on land, or with orbiting satellites. In someimplementations, the communications module 604 includes hardware and/orsoftware resources sufficient to implement data communication, including3G-, 4G-, WiMax-, or 5G-enabled communication equipment, among otherpossibilities. In some implementations, the communications module 604 isoperable to retrieve weather data for one or more points along thevessel's route, in addition to or instead of any weather-related onboardsensors in the sensor module 602.

The navigation system 600 includes an actuation module 606. Theactuation module 606 is operable to effect changes to the vessel'scourse, speed, or other parameters. This includes implementing changesto the vessel's course and/or speed based on conditions described hereinto mitigate slamming and/or rolling. In some implementations, theactuation module 606 can include middleware such as MOOS-IvP, maintainedby the Massachusetts Institute of Technology as part of the Laboratoryfor Autonomous Marine Sensing Systems; Robotic Operating System (“ROS”),maintained by Willow Garage, Inc.; and/or Control Architecture forRobotic Agent Command and Sensing (“CARACaS”), maintained by the NASAJet Propulsion Laboratory.

The navigation system 600 includes a computation module 608. Thecomputation module 608 is operable to take as inputs any of the variousmeasured quantities (e.g., inputs provided by the sensor module 602and/or external data sources via the communications module 604), andperform computations on those inputs. Such computations include, e.g.,the computations and/or comparisons described herein, including but notlimited to those described in connection with FIGS. 7 and 8.

Other implementations of the navigation system 600 are possible. Forexample, other implementations are described in U.S. Pat. No.10,467,908, entitled “Autonomous Boat Design for Tandem Towing,” theentirety of which is incorporated by reference herein.

FIG. 7 is a flowchart for a technique to mitigate slamming experiencedby a sea-faring vessel traveling at some nominal speed. The term“nominal speed” refers to the desired speed for the vessel in idealconditions. This speed may be pre-determined or dynamically determined,either manually or via automated means.

In step 702, a slamming parameter is measured. The slamming parameter isa numerical measure of the degree to which the vessel is currentlyexperiencing a slamming type of motion. In some implementations, theslamming parameter can include the vessel's pitch angle, or any timerate of change thereof. (Referring to FIG. 3, the rationale for thepitch angle or its rate(s) of change as a slamming parameter is that thegreater the distance d is, the greater variation the vessel's pitchangle and/or its time rate(s) of change will be as it traverses the wave202. On the other hand, the degree to which the vessel experiences aslamming-type motion also increases with d.)

Similarly, a slamming impact may be detected in other ways. For example,any force-sensing apparatus may directly measure the force with whichthe vessel's hull slams into the water below after traversing a wave.Alternatively, slamming the water may induce a strain across one or morecomponents of the vessel (e.g., its hull, one or more beams or portionsthereof, or any component mechanically coupled to both the bow and sternof the vessel). The induced strain, as detected by a strain gauge on thecomponent, may also correlate with the degree of slamming. Thus, in someimplementations, the slamming parameter may include: (1) the force withwhich a portion of the vessel (e.g., the vessel's bow) impacts thesurface of the water; (2) the distance d of FIG. 3 (e.g., as measured byan optical measurement device); (3) the vessel's heave or any time rateof change thereof (4) the strain experienced by a component of thevessel.

Yet other possible slamming parameters may be determined not based onthe motion experienced by the vessel, but rather the motion experiencedby a component thereof or object therein (including but not limited tocargo). For example, one or more accelerometers, gyroscopes, or forcesensing devices from the sensor module 602 may be coupled to an objectonboard the vessel; e.g., relatively sensitive cargo. Yet anotherslamming parameter may be determined by transient fluctuations in themeasured volume of fluid in a reservoir (e.g., fuel in a fuel tank).When undergoing slamming, the volume of fluid in the reservoir may sloshwithin the reservoir, which may be detected by volumetric sensors as abrief change in the actual volume, with more extreme slamming motiongiving rise to more extreme sloshing, and therefore more extremefluctuations in the measured fluid level. The magnitude of these changesmay be used as a slamming parameter.

In decision 704, it is determined whether the measured slammingparameter is within an acceptable range. In general, the acceptablerange of a slamming parameter depends on the particular vehicle and canbe set manually by an operator or other personnel associated with thevehicle. In some alternative implementations, decision 704 may involve acollection of measurements of different slamming parameters instead of asingle measurement. That is, decision 704 may determine whether astatistical quantity derived from a collection of measurements (e.g.mean, median, maximum or minimum value) falls outside the acceptablerange, whether at least some threshold number of measurements from acollection of measurements falls outside the acceptable range, etc.

If the slamming parameter is not in the acceptable range, then thevessel enters reduced speed mode (step 706), and the time at which thisoccurs is noted. If the vessel was already in reduced speed mode, thenthe time at which reduced speed mode was entered is updated to reflectthe time of the most recent measurement of step 702.

Upon entering or resetting reduced speed mode, the vessel's speed isdecreased (step 708). In some implementations, the vessel's speed isdecreased by a fixed amount, e.g. 5 knots. In some implementations, thevessel's speed is decreased to a fixed speed, e.g. 5 knots. In someimplementations, the vessel's speed is decreased by a proportion of itscurrent speed (e.g., 25%). In some implementations, the vessel's speedwill not be decreased below a certain minimum speed. In someimplementations, the minimum speed is 5 knots.

After decreasing the vessel's speed, the slamming parameter is measuredagain (step 702). In some implementations, the slamming parameter issampled 100 times per second. In some cases, the loop comprising steps702-704-706-708-702 continues until the slamming parameter enters anacceptable range (decision 704).

If it is determined in decision 710 that the vessel is not traveling atits nominal speed (i.e., its speed was recently decreased in at leastone traversal of the loop 702-704-706-708-702), then it is nextdetermined whether the vessel is in reduced speed mode (decision 712).

In some implementations, reduced speed mode may persist for apre-determined amount of time; e.g., 1 minute from the firstout-of-range parameter measurement, 1 minute from the most recentout-of-range parameter measurement, or some other time period. In someimplementations, reduced speed mode may persist only for as long as theslamming parameter is measured to be out of the acceptable range.

If the vessel is in reduced speed mode (decision 712), then the processreverts back to re-sampling the slamming parameter without increasingthe speed. On the other hand, if the vessel has exited reduced speedmode in decision 712, then the vessel's speed is increased (step 714).In some implementations the vessel's speed is increased a fixed amount(e.g. 5 knots) from its current speed. In some implementations, thevessel's speed is increased to a proportion of the vessel's nominalspeed (e.g. 50%). In some implementations, the vessel's speed isincreased by a proportion (e.g., 50%) of the amount of the most recentspeed reduction from step 708. In some implementations, the vessel'sspeed is increased by a proportion (e.g., 50%) of the total amount ofspeed reduction from the repeated iterations of loop702-704-706-708-702. In some implementations, the vessel's speed isincreased to its nominal speed. The amount of speed increase may dependon the number of iterations of loop 702-704-710-712-714-702.

FIG. 8 is a flowchart for a technique to mitigate rolling experienced bya sea-faring vessel traveling on some nominal course. The term “nominalcourse” refers to the desired course for the vessel in ideal conditions.In some implementations, the nominal course is determined manually, inadvance of the vessel's departure. In some implementations, the nominalcourse is determined dynamically, either manually or by automatic means.

In step 802, a roll parameter is measured. In some implementations, theroll parameter is vessel's roll angle or time rate(s) of change thereof.In some implementations, the roll parameter is the roll angle or timerate(s) of change of an object (e.g., cargo) onboard the vessel. In someimplementations, the roll parameter is the magnitude of a change in thevolume level of a fluid induced by sloshing, as described above.

In decision 804, it is determined whether the roll parameter is withinan acceptable limit. In some alternative implementations, decision 804may involve a collection of measurements instead of a singlemeasurement. That is, decision 804 may determine whether a statisticalquantity derived from a collection of measurements of the roll parameter(e.g. mean, median, maximum, or minimum value of the collection) fallsoutside the acceptable range, whether at least some threshold number ofmeasurements from a collection of measurements falls outside theacceptable range, etc. If the roll parameter is within an acceptablerange and the vessel is on its nominal course (decision 812), then thevessel continues on its course while the roll parameter continues to bemeasured. In some implementations, the roll parameter is measured 100times per second, and a sample window of 30 seconds is used. In someimplementations in which the roll parameter is the roll angle, theacceptable range can be set by the user. In some implementations theacceptable range is less than or equal to 20 degrees.

If the roll parameter is found to be outside the acceptable range indecision 804, then the vessel enters tacking mode (step 806), with aninitial tacking angle of 0 degrees. If a maximum tacking angle has notyet been reached (decision 808), then the vessel's course is adjusted bya pre-determined angle from the nominal course (step 810). In someimplementations, the maximum permitted tacking angle is 45 degrees. Insome implementations, the tacking angle is increased by a fixed numberof degrees in step 810, e.g. 15 degrees either to port or starboard. Insome implementations, the direction of the turn is such that the vesselturns into the wave, rather than away from the wave.

As discussed above with respect to FIG. 5, changing the tacking anglegenerally is effective to reduce the rolling parameter, thereby bringingit closer to the acceptable range. Thus, after possibly severaliterations of loop 802-804-806-808-810, either the vessel adjusts itscourse so that the rolling parameter is in an acceptable range, or themaximum tacking angle has been achieved.

Once either of these conditions occurs, the vessel proceeds on theupdated course. Referring to FIG. 9, in some implementations, there maybe further constraints on the vessel's updated course unrelated to rollmitigation. FIG. 9 is an overhead view of a vessel. The vessel 900 isinitially traveling towards a destination 902 on a nominal course 904.At some moment, the vessel 900 encounters rough conditions, causing itto identify an updated course 910. In some implementations, the updatedcourse 910 is a piecewise-linear course comprised of several lineartacking legs 909. A further constraint to the updated course is that, insome implementations, the vessel's updated course 910 must lie within apermitted navigation area 906. The permitted navigation area 906 may beidentified based on external sources (e.g., maps or other navigationcharts), or may be determined by real-time sensor data (e.g., depthsensors operable to identify areas of insufficient depth for the vessel;cameras or other optical sensors operable to identify other vessels orobstructions 908, etc.). In some implementations, there may be aconstraint on the maximum permitted length of a tacking leg, e.g. onehalf of a nautical mile. If the vessel has reached the maximum permittedtacking length, then it may begin a new tacking leg by turning 90degrees towards the nominal course 904 and resuming its journey. In someimplementations, the maximum permitted length of a tacking leg is afunction of the tacking angle. In particular, in some implementations,the tacking legs are of sufficient length that the midpoints of eachtacking leg coincides with the vessel's nominal course. While turning,there is the potential that the vessel is particularly vulnerable tooncoming waves; i.e., if the vessel 900 is oriented with respect to thewave as shown in FIG. 4. Thus, in some implementations, the 90 degreeturn is timed to begin directly after a wave's peak force is exerted onthe vessel 900. This peak force condition may be inferred from sensordata. In some implementations, the wave timing may be inferred fromoptical sources. In some implementations, the wave timing may beinferred from the vessel's motion. For example, when the pitch angle ofthe vessel encounters a local extremum (i.e., begins to decrease afterpreviously increasing, or begins to increase after previouslydecreasing), then the peak wave contact force may be inferred andturning maneuver may be executed. In some implementations, an additionalamount of thrust (e.g., 15%) may be applied to help execute the turn.

Referring back to FIG. 8, after potentially several iterations of loop802-804-806-808-810, the vessel may bring its roll parameter back intoan acceptable range in decision 804. Although the vessel will not be onits nominal course (decision 812), if the vessel remains in tacking mode(decision 814) it will continue to execute travel along successivetacking legs and execute successive turning maneuvers to traverse itsupdated course while completing possibly several iterations of loop802-804-812-814-802. After remaining in tacking mode for a time period,the vessel may test whether it is permissible to exit tacking mode. Insome implementations, this time period may be dynamically determined.For example, if the vessel is currently in weather/sea conditions thatare relatively stable, then the time period may be relatively long(e.g., 30 minutes). If the vessel is currently in weather/sea conditionsthat are likely to change rapidly, the time period may be relativelyshort (e.g., 5 minutes). In some implementations, such a test may beperformed by resuming the heading of its nominal course and measuringthe rolling parameter for another pre-determined time (e.g., 60seconds). If the rolling parameter is within the acceptable range, thevessel exits tacking mode and resumes its nominal course (step 816). Ifnot, the vessel re-enters tacking mode, executing subsequent loops ofFIG. 8 as appropriate.

In some implementations, the condition to exit tacking mode (or testwhether exiting tacking mode is permissible) may be determined bymeasurements, rather than the passage of a time interval. For example,updated weather data may indicate that the source of strong winds and/orwaves has subsided. In some implementations, this (or otherweather-related condition) may be used to determine whether it ispermissible to exit tacking mode, as described above.

The systems, methods, components, or other approaches described abovemay be implemented in software, or in hardware, or a combination ofhardware and software. The software may include instructions stored on anon-transitory machine-readable medium, and when executed on ageneral-purpose or a special-purpose processor implements some or all ofthe steps summarized above. The hardware may includeApplication-Specific Integrated Circuits (ASICs), Field ProgrammableGate Arrays (FPGAs), and the like. The hardware may be represented in adesign structure. For example, the design structure comprises a computeraccessible non-transitory storage medium that includes a databaserepresentative of some or all of the components of a system embodyingthe steps summarized above. Generally, the database representative ofthe system may be a database or other data structure which can be readby a program and used, directly or indirectly, to fabricate the hardwarecomprising the system. For example, the database may be abehavioral-level description or register-transfer level (RTL)description of the hardware functionality in a high-level designlanguage (HDL) such as Verilog or VHDL. The description may be read by asynthesis tool which may synthesize the description to produce a netlistcomprising a list of gates from a synthesis library. The netlistcomprises a set of gates which also represent the functionality of thehardware comprising the system. The netlist may then be placed androuted to produce a data set describing geometric shapes to be appliedto masks. The masks may then be used in various semiconductorfabrication steps to produce a semiconductor circuit or circuitscorresponding to the system. In other examples, alternatively, thedatabase may itself be the netlist (with or without the synthesislibrary) or the data set. A number of embodiments of the invention havebeen described. Nevertheless, it is to be understood that the foregoingdescription is intended to illustrate and not to limit the scope of theinvention, which is defined by the scope of the following claims.Accordingly, other embodiments are also within the scope of thefollowing claims. For example, various modifications may be made withoutdeparting from the scope of the invention. Additionally, some of thesteps described above may be order independent, and thus can beperformed in an order different from that described.

What is claimed is:
 1. A method of autonomously piloting a sea-faringvessel traveling on a pre-defined course at a nominal speed, the methodcomprising: measuring a slamming parameter of the vessel; determiningthat the slamming parameter is outside an acceptable range; andautonomously decreasing the speed of the vessel until the slammingparameter is within the acceptable range, thereby causing the vessel toenter a reduced-speed mode.
 2. The method of claim 1, in which theslamming parameter includes a time rate of change of heave of thevessel.
 3. The method of claim 1, in which the slamming parameterincludes a pitch angle of the vessel.
 4. The method of claim 1, in whichthe slamming parameter includes a slamming force experienced by thevessel.
 5. The method of claim 1, further comprising exiting thereduced-speed mode after expiration of a pre-determined time interval,wherein exiting the reduced-speed mode includes increasing speed of thevessel until either (a) the slamming parameter falls within theacceptable range, or (b) the vessel returns to its nominal speed.
 6. Amethod of autonomously piloting a sea-faring vessel traveling on anominal course, the method comprising: measuring a roll parameter;determining that the roll parameter is outside an acceptable range;autonomously determining an updated course that includes one or moretacking legs, in which each tacking leg makes a corresponding tackingangle with respect to the nominal course; and autonomously causing thevessel to traverse the updated course, thereby entering the vessel in atacking mode.
 7. The method of claim 6, in which each tacking angle ofeach tacking leg is determined by incrementing an intermediate tackingangle of the vessel until either (a) a maximum tacking angle is reached,or (b) the roll parameter is within the acceptable range.
 8. The methodof claim 6, in which the updated course includes at least one turningmaneuver, in which the turning maneuver is initiated immediatelyfollowing a peak in contact force of a wave on the vessel.
 9. The methodof claim 8, in which the wave contacting the vessel is detected by anoccurrence of a local extremum in a pitch angle of the vessel.
 10. Themethod of claim 6, in which the roll parameter includes a roll angle ofthe vessel.
 11. The method of claim 6, in which the roll parameterincludes a time rate of change of a roll angle of the vessel.
 12. Asystem comprising: a sensor module in data communication with one ormore processors, the sensor module operable to measure a slammingparameter of a sea-faring vessel traveling on a pre-defined course at anominal speed; and an actuation module in data communication with theone or more processors, the actuation module operable to effect a changein a course or a speed of the vessel; in which the one or moreprocessors are configured to: determine that the slamming parameter isoutside an acceptable range; and autonomously decrease the speed of thevessel until the slamming parameter is within the acceptable range,thereby causing the vessel to enter a reduced-speed mode.
 13. The systemof claim 12, in which the slamming parameter includes a time rate ofchange of heave of the vessel.
 14. The system of claim 12, in which theslamming parameter includes a pitch angle of the vessel.
 15. The systemof claim 12, in which the slamming parameter includes a slamming forceexperienced by the vessel.
 16. The system of claim 12, in which the oneor more processors are further configured to exit reduced-speednavigation mode after expiration of a pre-determined time interval,wherein exiting reduced-speed mode includes increasing the speed of thevessel until either (a) the slamming parameter falls within theacceptable range, or (b) the vessel returns to its nominal speed. 17.The system of claim 12, further comprising the sea-faring vessel.
 18. Asystem comprising: a sensor module in data communication with one ormore processors, the sensor module operable to measuring a rollparameter of a sea-faring vessel traveling on a nominal course; and anactuation module in data communication with the one or more processors,the actuation module operable to effect a change in a course or a speedof the vessel upon a determination that the roll parameter is outside anacceptable range; in which the one or more processors are configured to:autonomously determine an updated course that includes one or moretacking legs, in which each tacking leg makes a corresponding tackingangle with respect to the nominal course; and autonomously cause thevessel to traverse the updated course, thereby entering the vessel in atacking mode.
 19. The system of claim 18, in which each tacking angle ofeach tacking leg is determined by incrementing an intermediate tackingangle of the vessel until either (a) a maximum tacking angle is reached,or (b) the roll parameter is within the acceptable range.
 20. The systemof claim 18, in which the updated course includes at least one turningmaneuver, in which the at least one turning maneuver is initiatedimmediately following a peak in a contact force of a wave on the vessel.21. The system of claim 20, in which the wave contacting the vessel isdetected by occurrence of a local extremum in a pitch angle of thevessel.
 22. The system of claim 18, in which the roll parameter includesa roll angle of the vessel.
 23. The system of claim 18, in which theroll parameter includes a time rate of change of a roll angle of thevessel.
 24. The system of claim 18, further comprising the sea-faringvessel.